Transportation Research Record: Journal of the Transportation Research Board

The national Manual on Uniform Traffic Control Devices (MUTCD) does not prohibit the use of a pilot vehicle in conjunction with portable traffic control signals (PTCSs), but it does require that a flagger be stationed on the approach to the activity area where a pilot vehicle is being used. This negates the main advantage of using PTCSs—the removal of the flagger from the transition area. To assess compliance with pilot vehicles and PTCSs with and without flaggers, field studies were conducted at lane closures on two-lane, two-way roads in Texas. Only 2.7% and 2.3% of drivers did not comply with the PTCSs and pilot vehicle for both conditions studied (with and without a flagger, respectively). The similar violation rates between treatments showed that there was no significant or practical difference between violations at a PTCS with and without a flagger when a pilot vehicle was used. The overall recommendation is that the national MUTCD be changed to allow the use of a pilot vehicle in conjunction with PTCSs without a flagger at lane closures on two-lane, two-way roadways. In an effort to provide pilot vehicle drivers, especially those with less experience, an initial estimate of the minimum green time needed to clear the vehicle queue at the PTCS, an easy tool was developed.

Transportation agencies are considering public–private partnerships as they struggle to fund infrastructure and operations improvements. The national Manual on Uniform Traffic Control Devices (MUTCD) allows acknowledgments of private sponsors on static signs. The legibility and visibility impacts of including logos of sponsors on changeable message signs (CMSs) were examined. Thirty drivers participated in a closed-course study during daytime and nighttime conditions. Full-sized full matrix color LED signs were used to display travel time and safety reminder messages with and without sponsor acknowledgment logos. Single- and dual-phase messages were tested. The measures of effectiveness were legibility distance for target words on the signs and roadway hazard object detection distance. Legibility distances of the CMS messages were notably greater than those of retroreflective traffic signs and well above the MUTCD threshold of 30 ft/in. During the day, the median legibility index was approximately 60 ft/in. At night, the index was approximately 45 ft/in. Sponsor logos had no significant effect on the legibility distances of travel time signs. Sponsor logos had a small effect on the legibility distance of safety message signs with a blue background but not on those with a black background. The use of sponsor logos marginally affected object detection for certain object locations. The results of this study, coupled with an earlier driving simulation evaluation showing no cognitive distraction due to logos, support the use of sponsorship acknowledgment signs on CMSs. An open road evaluation is planned before statewide implementation is enabled.

Radar speed signs (RSSs) are a measure for reducing traffic flow speeds through work zones. The influence of truck-mounted RSSs on vehicle speed was evaluated for mobile maintenance operations in two multilane maintenance work zones in Oregon. In each case study, two periods of testing were conducted: one with the RSS display turned on (treatment) and one without the RSS display turned on (control), and vehicle speeds were recorded. Descriptive statistics were used to summarize collected data, and a two-sample t-test was applied to each case study to compare the speed difference between control and treatment cases. The findings indicate that vehicle speeds are typically lower and that there is less variation in speeds between adjacent vehicles with the RSS turned on. RSSs are thus promising devices for controlling vehicle speed and making work zones safer for motorists and workers.

Guidelines for the provision of effective nighttime performance of overhead signs were developed. Relevant policies and guidelines with regard to sign lighting currently provide little useful information to determine when sign lighting is needed, and the reference material available to practitioners is out of date. Two complementary nighttime visibility studies were conducted, which were designed to produce results useful in developing updated guidelines for overhead sign visibility. The first was conducted on a closed course and investigated the legibility distances of three sign legend and background configurations under various sign lighting treatments. The second was conducted on the open road. It investigated the effects of sign luminance and visual complexity on the distance at which a driver can read overhead signs during a recognition task. The combined findings were used to develop revised guidelines designed to provide adequate nighttime visibility of overhead signs. The proposed guidelines are based on the needs of nighttime motorists and have been formatted specifically for AASHTO’s Roadway Lighting Design Guide, which is being updated. The revised chapter on roadway sign lighting was provided to the AASHTO task force responsible for revisions. The guidelines include a list of recommended retroreflective sheeting materials that can be used to meet nighttime driver needs for specific complexity levels.

The regular auditing of installed roadway lighting performance is essential in ensuring that in situ light levels are within design specifications despite the effects of lamp deterioration or changes in roadway functional class. However, existing guidelines for measuring roadway lighting performance are tedious and often impractical for transportation agencies and municipalities, which are already faced with time and resource constraints. A method for calibrating a digital single lens reflex camera for rapid assessment of illumination levels at roadway intersections is developed in this paper. The method uses an image analysis approach to extract pixel information in a digital image and link it to the scene luminance. It uses high-precision light meters to perform an initial calibration of the digital camera that has proved to be stable over long periods. The method was tested with field data, and the results indicate that average scene luminance derived from this method differs by less than 4% from the average observed scene luminance captured by high-precision luminance meters involving a rigorous field measurement methodology. The methodology developed in this study offers transportation agencies and municipalities a rapid, inexpensive, and efficient method for auditing the adequacy of roadway illumination.

Nighttime crashes at work zones are major concerns for construction workers and motorists. Although in a majority of the U.S. states, department of transportation specifications for work zone lighting mention that contractors should reduce glare for workers and drivers, only two states advocate detailed specifications like light positions, orientation, and light levels. Although some studies have examined the impact of glare from work zone lights on workers and others have calculated veiling luminance levels for drivers in the work zone, the effect of work zone lighting on drivers’ visual performance and glare perception has never been studied in a realistic setting. The goal of this study was to understand the impact of commercially available portable light towers (metal halide, LED, and balloon) and their orientation on drivers’ visual performance and their perceptions of glare. Participants drove through a realistic work zone simulated on the Virginia Smart Road. Visual performance was assessed by a detection task and perception of visibility and glare were assessed by questionnaires. Results indicated that the type of light tower and its orientation affect visual performance and perceptions of visibility and glare. Light towers aimed toward the driver resulted in lowering drivers’ visual performance, both objectively and subjectively. When the light towers were aimed away from or perpendicular to the driver, the visual performance was higher and the differences in visual performance between the types of light towers were minimal. These findings indicate that these orientations should be preferred for work zone light towers.

Two work zone impact assessment methods were developed and their applicability was illustrated with data from recent construction projects on the I-35 Central Texas corridor. The first method was developed for postevent analyses of the impacts of freeway construction activities, incidents, and special events. The impacts were evaluated in terms of travel times and delay. An interval estimate for maximum queue length was also provided. Travel times and speeds were obtained by Bluetooth address matching. The method has also been used for determining work zone mobility performance measures, verifying the suitability of queue warning systems, and providing feedback for future deployment decisions. Based on more than 3 years’ experience with the analysis of impacts of road construction and maintenance projects as well as some major incidents on the I-35 corridor, the Bluetooth-based postevent closure analysis tool has proved to be very cost-effective. The second method was developed for determining the best closure schedule and start time for planned work zone lane closures. The best closure start time is the one that is expected to create the shortest queue lengths and has the least negative impact on travelers. The required input includes historical traffic volumes at a point upstream of the planned lane closure and estimated work zone capacity. The work zone capacity can vary over the duration of the work zone. The method runs input–output analysis in a dual-loop framework to analyze the impact of all available closure schedule scenarios and selects the best closure start time with the shortest expected queues.

Faced with a growing number of work zones, transportation agencies are being challenged to effectively manage the impacts of these zones, alleviate congestion, and maintain the safety of motorists and workers without disrupting project schedules. Coordinating work zones has already been practiced by various state departments of transportation and transportation agencies, yet there are no universal department of transportation policies that address how agencies should coordinate or consolidate projects. In addition, only a few states utilize computer tools specific to regional or corridor-based work zone coordination. State departments of transportation mostly coordinate significant and long-term projects. However, the majority of roadway projects include minor repair, roadway maintenance, bridge maintenance, surveying, and landscape and utility work that require relatively short-term work zones. The Work Zone Coordination Software tool was developed to provide the New Jersey Department of Transportation with an easy-to-use tool to evaluate the feasibility and effectiveness of coordinating short- and long-term work zones and to measure the benefits. This online tool is implemented with a web-based user interface. It integrates all scheduled and active construction projects, identifies conflicts between work zone projects, and estimates the benefits of conflict mitigation. The Work Zone Coordination Software tool works with the New Jersey work zone database by automatically importing data to provide up-to-date information to its users. However, the tool is built on a flexible framework that allows the integration of any work zone database provided that it includes all the required information.

Dynamic message sign (DMS) systems aim to provide realistic, reliable, and real-time traffic information to roadway users. This study investigated the performance of a DMS present at a work zone that warns drivers of any imminent congestion. A work zone in Davenport, Iowa, was used as the test site to evaluate the performance and the proposed algorithm improvements. A typical automated DMS uses a dedicated sensor measuring speed or occupancy and simple thresholds to post messages warning drivers of the congestion by using a set of predefined messages such as “Traffic Delays Possible,” “Slow Traffic Ahead,” and “Stopped Traffic Ahead.” On the basis of field observation, it was found that these simplistic algorithms lead to a significant number of very short messages, erroneous messages during nighttime, and groups of messages that continuously alternate between different displays. This study first developed performance metrics to report the issues with the existing DMS automated programming logic and then proposed a machine learning–based real-time algorithm for improved operations.

Roadway lanes are often repositioned to accommodate highway work operations; as a result, pavement markings need to be altered. Although there are various methods for removing or obscuring existing pavement markings, “ghost” markings often remain at the locations of the old lane lines. These ghost markings can be quite conspicuous under certain lighting conditions, creating the potential for road user confusion. The Canadian province of Ontario and several European countries routinely use a special marking color (orange or yellow) to increase the salience of temporary lane lines. Special-color markings have also been used experimentally in Australia; New Zealand; Quebec City, Canada; and the United States. As a first step toward identifying the benefits and risks of special-color markings, existing practices from several countries are reviewed and summarized. The review identified a significant policy difference among jurisdictions: in some jurisdictions special-color markings override existing markings (so that the old markings are left in place), whereas other jurisdictions use special-color temporary marking but also attempt to remove old lane lines. The recent special-color marking demonstration projects in Australia, Canada, New Zealand, and the United States have been on major freeways, but European practice suggests that special-color marking could have significant benefit for urban arterial streets.

Work zone temporary traffic control strategies generally affect both traffic safety and operations. However, there is a substantial gap in the knowledge base with respect to the safety impacts of various work zone characteristics. The Highway Safety Manual provides crash modification functions that account for the effects of project length and duration on crash frequency as compared with normal road operations. However, these methods do not allow for explicit comparisons of expected safety performance among different work or closure types. This research examined the safety impacts of various temporary traffic control strategies on freeways, including shoulder closures, lane closures, and lane shifts. Data were collected for the periods during which these treatments were in effect and during similar nonconstruction periods from the preceding year. Safety performance functions were estimated that account for segment length, duration, traffic volume, and closure type. Random parameter count data models were estimated to accommodate segment-specific temporal correlation and unobserved heterogeneity. Crash rates were shown to vary roughly in proportion to traffic volumes. In contrast, segment length and project duration showed inelastic effects; this finding implies that crash rates increase more rapidly in work zones that are shorter in length or duration. Single-lane closures, multilane closures, and lane shifts were associated with an increase in crashes, whereas shoulder closures did not show a significant difference compared with similar, non-work-zone conditions. Ultimately, the study results provide important information that can be used to assess the crash risk for various temporary traffic control strategies.